Monteiro began racing in 1997 in the French Porsche Carrera Cup, winning the B-class title and the rookie of the year award. He then competed in the French Formula Three Championship from 1998 to 2001, finishing runner-up in both 2000 and 2001. During this period he also raced at Le Mans, finishing seventeenth overall and sixth in the GT2 class in 1999. His 2000 campaign included second place in a Formula 3 European Championship double-header at Spa-Francorchamps.
In 2002 Monteiro raced in the F3000 Championship with Super Nova, and in 2003 he moved to the Champ Car World Series with Fittipaldi Dingman Racing, achieving a front row start at Mexico City and recording ten top-ten finishes for fifteenth in the championship. He served as a Minardi F1 test driver in 2004 while competing in the Nissan World Series with Carlin Motorsport, finishing second in the championship behind Heikki Kovalainen and earning Rookie of the Year honours.
Monteiro was signed by Jordan Grand Prix for the 2005 Formula One season alongside Narain Karthikeyan, making his debut at the Australian Grand Prix. His most notable moment came at the United States Grand Prix at Indianapolis, where tyre safety concerns led all Michelin-shod teams to withdraw from the race. With only the three Bridgestone-equipped teams competing, Monteiro finished third from six starters, becoming the first Portuguese driver to stand on a Formula One podium. He celebrated alone on the podium after the Ferrari drivers made a swift exit, earning a round of applause from the partisan crowd. He also established a new record for consecutive finishes by a rookie driver that season, completing all of his races up to the Belgian Grand Prix.
Monteiro remained with the rebranded Midland team in 2006, partnering Christijan Albers in the M16. The car was uncompetitive throughout the year and he failed to score a point, with his best result being ninth at the Hungarian Grand Prix. At the season's end he was replaced by Adrian Sutil at the renamed Spyker team. Monteiro departed Formula One with one podium and seven championship points, the best of any Portuguese driver in the series at that time.
Monteiro joined SEAT Sport for the 2007 WTCC season, taking three podiums and a pole position in his debut campaign. In 2008 he claimed his first WTCC victories, winning at Puebla in Mexico and at his home event in Estoril, Portugal. Further wins followed at Portimão and Valencia in 2010, his strongest season in the SEAT-backed Sunred Engineering squad, in which he finished fifth overall.
Monteiro joined the Honda Racing Team JAS from the 2012 Race of Japan onwards, scoring the first WTCC podium for the Honda Civic at the Guia Race of Macau later that year. He won with Honda at Shanghai in 2013, helping the manufacturer claim the World Manufacturers' Championship. He added wins in Russia and Japan in 2015 and victories in Slovakia and Portugal in 2016. In 2016 he achieved his best championship result, finishing third overall behind José María López and Yvan Muller.
In 2017 Monteiro was leading the championship after twelve rounds when a brake failure during testing at Barcelona caused a serious accident that ended his season prematurely. He spent much of 2018 recovering and made a partial return at the penultimate WTCR round at Suzuka in November. He returned full-time in 2019, winning his home race in Portugal at the WTCR. He also won the Nürburgring 24 Hours in the TCR class in both 2019 and 2020. Monteiro competed through the final three seasons of the World Touring Car Cup before the series folded after 2022.
In November 2008, Monteiro purchased the BCN Competición team in the GP2 Series, renaming it Ocean Racing Technology. The team competed in GP2 and GP3 from 2009 until 2012, when it withdrew due to funding shortfalls. Monteiro also manages the career of fellow Portuguese driver António Félix da Costa, who won the Formula E World Championship in 2019–20.